[Effects of sutures on rat corneas].

Cellular infiltration of the suture line was studied immunohistologically after rat corneas were sutured with various types of suture materials. The suture line was invaded by helper/inducer T lymphocytes, cytotoxic/suppressor T lymphocytes, and Ia-antigen-positive cells. Among the invading cells, Ia-antigen-positive cells were the most prominent over an extended period of time from immediately after suture placement. The helper/inducer T lymphocytes consisted predominantly of cytotoxic/suppressor T lymphocytes. The 9-0 silk suture produced a higher degree of cellular infiltration than the 10-0 nylon suture or the 10-0 prolene suture. There was no marked difference in the infiltration produced by the 10-0 nylon and 10-0 prolene sutures. After the sutures were removed, the cellular infiltration appreciably decreased. More marked invasion occurred with interrupted sutures than after the inter-lamellar insertion of suture material. These findings indicate that suture materials on the cornea promote infiltration of immunocompetent cells and that mechanical stimulation of the suture notch enhances such cellular response, which may be involved in graft rejection of the corneal transplantation.

The micronucleus test and erythropoiesis. Effects of erythropoietin and a mutagen on the ratio of polychromatic to normochromatic erythrocytes (P/N ratio).

It is considered that a decrease of the ratio of polychromatic erythrocytes (PCE) to normochromatic erythrocytes (NCE) (P/N) in the micronucleus test is an indicator of bone marrow toxicity induced by mutagens. However, the exact meaning of fluctuation in the P/N ratio is not yet known. We have studied this point by counting the total number of erythrocytes and nucleated cells in the bone marrow following various treatments. The P/N ratio decreased gradually with time after administration of mitomycin C. Our data suggest that the decrease of P/N ratio was attributable to an increase in the numbers of the denominator, i.e. NCE, caused by rapid differentiation and multiplication or denucleation of erythroblasts which remained in the bone marrow instead of entering the peripheral blood stream. A decrease of P/N ratio was also observed in the early phase after administration of erythropoietin, an agent which induces differentiation and multiplication of erythroblasts. This phenomenon might result from an increase of PCE delivery into the blood circulation. However, following the initial decrease, the P/N ratio increased gradually 48 h after administration of erythropoietin. It is supposed that this increase probably resulted from an increase in PCE in the bone marrow due to the direct effects of erythropoietin on erythropoiesis. The drastic change in erythropoiesis in the bone marrow induced by either mutagen or erythropoietin treatment will affect the fluctuations of the P/N ratio or the number of micronucleated erythrocytes per non-micronucleated erythocytes in the micronucleus test. This contrasts with the original explanation for such fluctuations which attributed them to replenishment of the marrow by peripheral blood.

[Study of mutagenicity of epoxy resin hardeners by fluctuation test].

Mutagenicity of nine epoxy resin hardeners was examined by a fluctuation test modified by Gatehouse. The test was performed by using Salmonella typhimurium TA98 with a metabolic activation system. In our laboratory, the results of the fluctuation test were compared with the results obtained by the previously mentioned Ames preincubation method. Six out of nine epoxy resin hardeners showed mutagenic activity in both the fluctuation test and Ames preincubation method, but one out of the nine was negative in both test systems. Two out of the nine were positive by either of the two testing systems. The fluctuation test is disadvantageous in that it is marginally slower and requires slightly more labor than the Ames test and furthermore it is difficult to increase the amount of microsome because of background interference. These disadvantages, however, are somewhat offset by the advantages that small organs such as urinary bladder can be used instead of liver cells and that a small amount of microsome can be employed for metabolic activation. This test is also suitable for testing aqueous samples containing low levels of mutagen.